Case 9: Earthquake Occurrence and Temporal Variations in Earth Tidal Strain Amplitudes
- Max Wyss
Published Online: 3 APR 2013
Copyright 1991 American Geophysical Union.
Evaluation of Proposed Earthquake Precursors
How to Cite
Yamauchi, T. (1991) Case 9: Earthquake Occurrence and Temporal Variations in Earth Tidal Strain Amplitudes, in Evaluation of Proposed Earthquake Precursors (ed M. Wyss), American Geophysical Union, Washington, D. C.. doi: 10.1029/SP032p0061
- Published Online: 3 APR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875907840
Online ISBN: 9781118667873
- Earthquake prediction—Evaluation
The temporal variations of tidal strain amplitudes at the Mikawa Crustal Movement Observatory, in central Japan, were investigated in detail using the strain data recorded with three silica-tube extensometers. The daily amplitudes of semi-diurnal tide M 2 were calculated by the Fourier analysis from many series of 30 days' data which were obtained by shifting the data successively step by step every day. The standard deviations of the amplitudes of M 2 from each detector usually remain within 5%, but sometimes the variations clearly exceed standard deviation. Such abnormal variation in tidal strain amplitude appeared four times from January 1974 to December 1987. The largest variation of the amplitude was found before the earthquake of March, 1983 (M = 5.7, Δ = 14 km, h = 40 km) which occurred near Lake Hamana. The appearance of these abnormalities seems to be related to the earthquake occurrence around the coastal line. The observed results suggest that the abnormal variations in the tidal strain amplitude are probably reflecting the changes in the crustal properties in the earthquake source regions.